Optical resonators are employed in photonic systems in a wide variety of ways including, but not limited to, in signal modulation, signal detection, signal switching and routing (e.g., on/off switching, add/drop switching, etc.), and even as light sources (e.g., in laser cavities). For example, an optical resonator coupled to a bus waveguide is often used to selectively block passage of optical signals having a particular wavelength, while optical signals at other wavelengths may be passed through the bus waveguide substantially unaffected. In particular, an optical resonator having a resonance corresponding to a first wavelength may selectively couple from the bus waveguide an optical signal with the first wavelength. The selectively coupled optical signal may be absorbed by the optical resonator, for example, and therefore not proceed in the bus waveguide. However, optical signals at other wavelengths may not be coupled from the bus waveguide and thus may be substantially unaffected by the optical resonator. Being substantially unaffected by the optical resonator, these other optical signals may continue to propagate along the bus waveguide. In another example, the optical resonator may selectively couple an optical signal having the first wavelength out of a first coupled bus waveguide and into second coupled bus waveguide, while other optical signals having other wavelengths remain in the first bus waveguide.
In many photonic circuits that employ optical resonators, optical resonator modulation is often useful or even important to the performance of the photonic circuit. In particular, performance of the optical resonator (e.g., resonance wavelength) may be varied in situ to control an input/output (I/O) characteristic of the photonic circuit that employs the optical resonator. Typically, optical resonator modulation is provided by modulating the optical resonator itself. In particular, a length of a cavity or equivalently a resonance wavelength of the optical resonator may be varied to provide the modulation. For example, a resonance wavelength of a ring resonator may be varied by changing or varying a modal index of an optical waveguide that makes up the ring resonator. The modal index may be varied by applying an electric field to a material of the ring resonator optical resonator, for example. However, modulating the resonance wavelength the optical resonator may be difficult to implement, may involve relatively highly energy consumption, and further may exhibit fundamental limitations associated with modulation bandwidth or speed of modulation.
Certain examples have other features that are one of in addition to and in lieu of the features illustrated in the above-referenced figures. These and other features are detailed below with reference to the above-referenced figures.